In general, thermoelectric cooling devices are solid state heat pumps that are used in a variety of applications where thermal management is required. For instance, thermoelectric cooling modules are implemented for actively cooling electronic components such as semiconductor IC (integrated circuit) chips. By way of example, FIG. 1 schematically illustrates a conventional apparatus (100) for cooling an electronic device. In general, the apparatus (100) comprises a thermoelectric (TE) module (101) that is thermally coupled between an electronic device (102) (e.g., IC chip) and a heat sink (103). The TE module (101) can be electronically operated to transfer heat from the electronic device (102) (heat source) to the heat sink (103) (cooling effect) by applying a DC voltage (104) to the TE module (101) with proper polarity.
In particular, the TE module (101) comprises a plurality of bulk thermoelectric (TE) elements (105), which are connected electrically in series and thermally in parallel. The TE elements (105) comprise alternating n-type TE elements (105a) and p-type TE elements (105b) that are electrically connected via respective interconnects (106). The TE elements (105) and electrical interconnects (106) are mounted between two thermally conductive ceramic substrates (107) which hold the TE module (101) together mechanically and which electrically insulate the TE elements (105).
Typically, the TE elements (105) are formed of bulk n/p-doped semiconductor bismuth telluride (Bi2Te3) elements. The n-type TE elements (105a) are doped with an excess of electrons and the p-type TE elements (105b) are doped with an excess of holes. The TE module (101) can have an equal number of n-type and p-type elements and each n-type/p-type TE element pair (105a, 105b) forms a TE couple element. Conventional TE modules such as depicted in FIG. 1 typically can have one to several hundred TE couples.
The cooling capacity of the TE module (101) is proportional to the magnitude and polarity of the DC current applied via DC source (104) and the thermal conditions on each side of the module (101). By applying a DC voltage to the TE module (101) having the polarity as depicted in FIG. 1, heat can be transferred by the TE module (101) from the device (102) to the heat sink (103). The electrons and holes are the carriers that move the heat energy through the TE module (101). By applying a direct current through the TE elements (105) as shown, both the electrons and holes are moved from one side of the TE module (101) to the other side of the TE module (101) through the TE elements (105), while electric current flows back and forth between the two junctions of TE module (101) and alternately through each n-type TE element (105a) and p-type TE element (105b).
In particular, the transfer of heat energy is due to the Peltier effect, where heat is absorbed at one junction (e.g., the junction between the module (101) and the device (102)) to compensate for the loss of charged carriers and generate additional pairs of electrons and holes, while heat is released at the other junction (e.g., the junction between the TE module (101) and the heat sink (103)) as the electrons combine with holes. More specifically, as depicted in FIG. 1, both holes (+) and electrons (−) move through the TE elements (105) away from the junction between the TE module (101) and the device (102), toward the junction between the TE module (101) and the heat sink (103), as a consequence of the DC current flow through the junction. Holes move through the p-type elements (105b) and electrons move through the n-type elements (105a) toward the heat sink (103). To compensate for the loss of charge carriers, additional electrons are raised from the valence band to the conduction band to create new pairs of electrons and holes. Since energy is required to do this, heat is absorbed at the junction between module (101) and the device (102). Conversely, as an electron drops into a hole at the other junction, surplus energy is released in the form of heat.
The direction of the heat flow depends on the polarity of the DC voltage (104) applied to the TE module (101) such that heat can be pumped through the TE module in either direction. Consequently, the TE module (101) may be used for both heating and cooling, which makes it suitable for applications that require precise temperature control. Furthermore, the TE module can be used for power generation, as a result of the Seebeck effect, where a current is generated due to the temperature differential across the TE module.